Converting the energy stored in hydrocarbons back to electrical energy can be done with the current technology at efficiencies well over 50% using Diesel engines.

Higher efficiencies can be reached with fuel cells. It is true that for now, especially for room-temperature fuel cells, much more research has been done for fuel cells with hydrogen.

However room-temperature fuel cells are handicapped anyway by the need for expensive catalysts. High temperature fuel cells can be made to work almost as well with hydrocarbons as with hydrogen. Their lifetime needs improvement, but it is likely that better results could have already been obtained if the research efforts in energy conversion would not have so dispersed over a very large number of directions, most of which were obviously wrong since the beginning.

Right now it is indeed possible to obtain hydrogen from water with a higher efficiency than hydrocarbons, because it can be done in a single simpler step, the electrolysis.

Nevertheless, in an optimized synthesis, the efficiency of obtaining hydrocarbons instead of hydrogen, also sequestering carbon dioxide as an added benefit, should have a very close efficiency, as proven by the countless bacteria that do a similar job.

It is possible right now to capture carbon dioxide and store energy in synthetic hydrocarbons, then generate electrical energy from the stored hydrocarbons.

However the cost and efficiency of doing that would be much less than desirable and possible.

That is why I said that this would require much more R&D than now, but this would be a certain solution for the long term storage problem.

For short term storage, high-efficiency solutions, e.g. flow batteries, pumped water, compressed air and so on, are better solutions.